This invention relates to apparatus for circulating fluid and in particular, apparatus for circulating fluid in a well riser, and to a method of cleaning same using the apparatus.
A number of forms of cleaning equipment or apparatus are known for cleaning out the inside of a well casing or liner to wash away any debris or other contaminants. However, apparatus and method suitable for cleaning well risers above the seabed are less common and generally unsatisfactory. This, in part, is because of the relatively large internal diameter of typical risers, rendering most known equipment impractical for this purpose.
One type of clean-up apparatus is known as a circulating tool. This apparatus relies on the use of high flow rates to create turbulence to aid the cleaning out process.
In British Patent Number 2,272,923, there is described a multifunction circulating tool. The tool has an axial through passage between an inlet and a first outlet, the inlet and the first outlet being adapted for connection in a drill string supported from the surface, a second outlet extending generally transversely of the apparatus, wherein the apparatus includes an obturating member movable between a first position closing the second outlet and a second position permitting fluid flow through the second outlet; and in which the apparatus is associated with a shoulder engageable with a shoulder portion in the borehole.
Typically, said formation in the borehole is defined by the top edge of a liner within the borehole and the shoulder is connected to the obturating member. However, the application of the top edge of the liner as the formation is not entirely or always suitable when it is desired to flush or is clean the well riser.
An object of the present invention therefore is to provide a method for using this known circulating tool to clean well risers.
According to the present invention there is provided a method of cleaning a well riser, the method comprising suspending in a drill string from surface a circulating tool in the well riser, and causing the circulating tool to axially collapse so as to open one or more radial outlets in the tool and allow cleaning fluid to be expelled out of the tool and impact on the inside of the well riser.
Typically the well riser is provided with blow out preventers incorporating drill string rams and the circulating tool is caused to axially collapse by closing the drill string rams around the drill string below the circulating tool and slacking off sufficient drill string weight to hang the drill string and collapse the tool.
Alternatively, the tool may be provided with a shoulder which co-operates with a formation in the well riser to allow for the slacking off of sufficient drill pipe weight to hang the pipe and collapse the tool.
The method may further include passing the cleaning fluid down the drill string to an inlet of the apparatus and thence via a first outlet communicating with the drill string below the circulating tool before setting down the weight of the drill string.
The method may be employed after drilling or milling is complete and include pulling the drill pipe upward and out of a well bore until the tool is above the drill pipe rams.
According to a second aspect of the present invention there is provided a circulating tool for cleaning well risers, the tool comprising a generally axial body having an axial through passage between an inlet and a first outlet, the inlet and the first outlet being adapted for connection in a drill string supported from the surface, a second outlet extending generally transversely of the tool, wherein the tool further includes an obturating member movable between a first position closing the second outlet and a second position permitting fluid flow through the second outlet.
The drill string may be provided with a shoulder for cooperating with a formation in the well bore or riser. The shoulder may be provided as part of the circulating tool.
Preferably, the second outlet comprises a number of apertures in a body member which communicate with the inlet and typically, the apertures may be distributed circumferentially around the outer surface of the body member.
Typically, the cross-sectional area of the first outlet is greater than the cross-sectional area of the second outlet.
Preferably, the second outlet is designed to communicate with the apertures in the sleeve irrespective of the circumferential orientation of the sleeve with respect to the second outlet. This could be designed by providing a circumferentially extending groove on the inside of the obturating member which aligns with the second outlet when the second outlet is open.